1. Field of the Invention
This invention relates to composite porous structures having a matrix component of large pore size which confines a polyvinylchloride component of small pore size.
2. Description of the Prior Art
In the field of pollution control, it is often sought to remove toxic organic substances from water. The organic substances may be present in dissolved or suspended form, and may be present in large amounts, or in small amounts such as in parts per million, parts per billion, or less. Exemplary toxic organic species include: polychlorinated biphenyls, dioxins, polyaromatic hydrocarbons, nitroaromatics, pesticides, herbicides, and volatile halocarbons.
Current technology for removing such organic contaminants involves the use of activated carbon. However, the activated carbon, generally in granular form, must be confined within a vessel as a bed through which the water to be treated is caused to flow. The bed of carbon granules generally creates impedance to the water flow, requiring adequate pumping to achieve a sought flow rate. Also, suspended material in the in-going water stream may accumulate within the bed to cause even higher flow impedance. Although activated carbon functions efficiently, its total capacity for absorbed species is low, often less than 2% of the weight of the carbon. This results in the need to handle large amounts of carbon for the removal of relatively small amounts of contaminants.
Another problem in the field of pollution control is filtration for the removal of extremely fine suspended particles. Classic filtration methods employ, for example, sand bed filters and plate and frame presses. Such equipment is of large size and considerable expense, and requires careful monitoring to assure proper performance. Filters involving a porous membrane are usually employed for removing small quantities of very fine particles that may have passed through conventional filters. The membrane filters, however, are easily clogged or xe2x80x9cblindedxe2x80x9d when relatively little material accumulates on the upstream surface of the membrane.
The use of a microporous form of polyvinyl chloride (PVC) in filtration applications has been disclosed in U.S. Pat. No. 3,674,722. Although the microporous PVC performs well in filtration applications, it is difficult to produce useful shaped structures from the microporous PVC because of shrinkage during molding. Also, such shaped structures have been found to be brittle. When the shaped structure involves a continuous smooth upstream filtration surface, the microporous PVC filter clogs as easily as less expensive membrane filters.
It is disclosed in said U.S. Pat. No. 3,674,722 at column 3, lines 41-42 that the microporous PVC can be inserted as an impregnant into a macroporous matrix such as an open celled foam. It has been found however, that without a critical selection of the nature of the macroporous matrix and the process of incorporation of the PVC, the PVC tends to flake away from the matrix. Such is particularly the case with rigid or flexible foams or sponges comprised of polyethylene, polyurethane, polystyrene, phenolics, and silicones. In particular, it has been found that matrices comprised of hydrophilic material are best suited for retention of the microporous PVC.
It is accordingly an object of the present invention to provide a process for producing a composite porous structure capable of absorbing organic pollutants from water.
It is another object of this invention to provide a process for incorporating microporous PVC into a macroporous matrix to produce a composite porous structure as in the foregoing object.
It is a further object of the present invention to provide a process for producing a composite porous structure of the aforesaid nature capable of filtering suspended particles out of water.
It is another object of this invention to provide a low cost process for producing a composite porous structure of the aforesaid nature.
These objects and other objects and advantages of the invention will be apparent from the following description.
The above and other beneficial objects and advantages are accomplished in accordance with the present invention by a process for producing a composite porous structure capable of absorbing organic pollutants from water comprising:
a) preparing a dispersion of non film-forming PVC particles in a water-soluble organic liquid which is a non-solvent for PVC and is relatively non-volatile,
b) impregnating said dispersion into a macroporous matrix of a hydrophilic material, and
c) subjecting said impregnated matrix to an elevated temperature to achieve sintering of said particles to produce a microporous PVC substrate which is retained within said macroporous matrix.